The Light Emitting Diode (LED) is a light emitting device. Similar to a diode, LED consists of a semiconductor material, and the doped and implanted impurities therein create a p-n junction. When voltage bias is applied across the p-n junction, the current flows from the p-side, the anode, to the n-side, the cathode, and the charge-carriers, electrons and electron holes flow into the junction from the anode and cathode, respectively, and meets each other. Then the electron falls into a lower energy level, and releases a photon, that is lighting. The LEDs have benefits in their low operating voltages, small power consumptions, high-efficiency light emitting, extreme short emitting response time, pure light color, firm structures, anti-impact, anti-vibration, stable and reliable performances, light and small bodies, and low cost, etc. The development in LEDs is prompt, and it is now capable of manufacturing high-illuminant and high-performance LEDs for emitting light of all colors in the visible light spectrum in mass production. The LED manufacturing process includes the upstream processes for manufacturing the epitaxial layers of the LEDs, while the middle-stream processes includes the chip design and wafer dicing process, and the downstream processes includes the packaging and testing of the LEDs. The quality of the final LEDs product is greatly depending on the package technology. The conventional packaging of the LEDs includes two types: the circuit type and the lead-frame type. The circuit-board type process uses circuit boards made of composite material as substrates to be compression molded so as to package the LEDs. In the lead-frame type process, a metallic lead frame is used as the substrate, and the packaging is performed by injection molding or compression molding. However, the LEDs produced by this two packaging methods have common defects such as deficient heat resistances and poor heat dissipations, etc.
Therefore, a process for forming a LED packaging substrate is developed and disclosed in U.S. Pat. No. 6,531,328. The steps for this method are illustrated in FIGS. 1A-1G. Firstly, as shown in FIG. 1A, a silicon substrate 1 with (100)-oriented lattice structure is provided. Then, as indicated in FIG. 1B, a photoresist 10 is applied on one side of the silicon substrate 1. A photolithography process is then executed so that the photoresist in area 11 (see FIG. 1C) is removed. FIG. 1D indicates that etched grooves 12 are formed by wet etching the substrate 1. Each of the etched grooves 12 has an inclined wall with an inclined angle of 54.74°. In FIG. 1E, the photoresist 10 is removed. After then, another photoresist is applied on the other side of the silicon substrate. The photoresist is then exposed and developed to define a semi-through hole and a through-hole pattern in respective aligned relationship with the etched groove 12. The semi-through hole pattern and the through-hole pattern are then dry-etched to form the semi-through hole 14 and the electrode holes 15 through the silicon substrate. After removing the photoresist from the silicon wafer substrate, the structure of the substrate 1 made by silicon is shown in FIG. 1F. The final steps include forming an insulation layer 16 on the front and back sides of the substrate 1 by oxidation or nitridation; and applying a conductive metal layer 17 by electroplating to the front and back sides of substrate 1 and inside electrode holes 15. The LED packaging substrate, as shown in FIG. 1G, is then formed.
However, in the process of manufacturing the above-mentioned conventional LED packaging substrate structure, wet/dry etchings are needed to etch the front/back side of the silicon substrate. Therefore, the process needs complex steps to perform the manufacturing of the packaging substrate, which also increases the cost. Furthermore, many of the products manufactured by the above-mentioned method cannot conduct current normally. That is because an unpredictable fault phenomenon may happen when applying the conductive layer 17 on the electrode hole 15, which will reduce the yield of the packaging of the LED grain on the substrate 1. Furthermore, when welding the packaged LED to the printed circuit board, some solder may overflows from the rear side 19 of the silicon substrate 1 to the lateral side 18, which will cause an leakage current. Therefore, the above-mentioned defects are intended to be improved by the present invention.